Method for the removal of monomers, etc., from molten polymers



SP e 1 5 I... L. MALM 2,904,109

METHOD FOR THE REMOVAL OF MONOMERS, ETC., FROM MOLTEN POLYMERS Filed March 50. 1953 v 2? CONDENSER uvvsurok LAWRENCE Lou/s MALM a) M/ ATTZ/VEY United States Patent METHOD FOR THE REMOVAL OF MONOMERS, ETC., FROM MOLTEN POLYMERS Lawrence Louis Malm, Rocky River, Ohio, assiguor to Industrial Rayon Corporation, Cleveland, Ohio, a corporation of Delaware Application March 30, 1953, Serial No. 345,623

2 Claims. (Cl. 159-49) This invention relates to the production of shaped articles such as filaments, monofils, bristles, films and the like from nylon 6 type polyamide polymers. More particularly, it relates to a process of melt spinning polyamides produced by the polymerization of lactam monomers, e.g., epsilon-amino caprolactam hereinafter referred to as e-caprolactam.

In the polymerization of e-caprolactam it is known that the polymerization reaction does not proceed to completion and that at the end of the polymerization reaction a state of equilibrium exists between the polymer and the monomeric or dimeric lactam wherein the polymerization product contains up to about 10% of the unpolymerized lactatns.

It is also known that the presence of undesirable quantities of lactam monomers in the extruded shaped articles, hereinafter referred to as yarn, present spinning and processing difficulties. Thus, it may be necessary to interrupt a continuous process operating at increased rates with slow and expensive washing steps prior to or after extrusion. Also, there is a loss of yarn strength caused by the handling of such lactam containing yarns, e.g., during the transfer of such yarns from bobbins, over guides or during stretching and rewinding operations.

Heretofore there have been a number of proposals for meeting the problems created by the presence of exces- Sive lactam in either the spinningmelt or in the extruded product. In one proposal the polyamide melt containing excessive lactams is first converted into solid chips, ribbons or beads and the latter washed with warm water to extract the water-soluble lactam and the resulting washed polymer thereafter subjected to an expensive drying operation. In addition to the disadvantages arising out of the expense of this proposal, it is found that monomeric lactam is reformed when the extracted chips are again melted and maintained at the melt temperature prior to extrusion. Thus, a depolymerization reaction takes place in which up to 5% or more of the lactam is reformed depending upon the length of time it is maintained in the fluid melted state.

In another proposal the polymer containing excessive lactam is melt-spun and the resulting solidified yarn is coated with a lubricant so as to prevent filament breakage as the yarn passes over handling means such as guides, spools, etc. during the subsequent processing steps, e.g., stretching, packaging, unwinding, etc. More specifically, the filament breakage referred to is caused by the accumulation of the lactam (a white solid having a melting point of 68 C.) on the handling or guiding means as the yarn passes thereover. Accordingly, the lubricant is added to reduce the amount of hard deposits formed on the guides or other associated yarn contacting devices. This proposal, however, does not provide a satisfactory solution to the problem. The yarn damage caused by the lactam deposits is not sufficiently eliminated and, in addition, the presence of the lubricant on the yarn renders it more diflicult and expensive to leach out the lactam from the fiber. Moreover, the presence of the lubri- "ice cant increases both the cost of the process and the cost of recovering the lactam from the wash waters.

In accordance with the present invention, a melt spinning process has been discovered which not only avoids the necessity of forming and washing polymer solid chips, etc., prior to extrusion, but also successfully avoids the loss of yarn strength because of excessive or undesirable quantities of lactam monomers. The process of the present invention may be performed as follows. The fluid melt of the polymer containing excessive or undersirable proportions of the lactam monomers, dimers, etc., is converted prior to spinning into the form of a continuous spreading flow in an enclosed vessel; the flow into the vessel being advantageously effected by an inert gas, such as nitrogen, under pressure, into an expanding chamber having a large area or surface over which the continuously charged melt spreads as a thin film. The excess or undesirable quantities of lactam monomers, etc., that rise and that are released by the nitrogen and that evaporate from the thinned exposed melt surface are continually removed or exhausted from the chamber. The flow of polymer is, meanwhile, continuously subjected to a sparging action of superheated steam which also assists greatlyvin removing rising lactam monomers, etc., and any vapor that is given off, and this mixture of gases being continually evacuated. The exhaust steam and vapor are subsequently condensed in a zone removed from said melt thereby removing the extracted monomers from the melt.

The process is further more specifically illustrated and described in the following specification and accompanying drawing, where; v

The drawing is a schematic arrangement of an apparatus which is advantageously adapted for de-monomerizing a polyamide melt.

Referring to the drawing a source of polymer melt 10 continually supplies melt to a chamber 12. Into chamber 12 extends conduit13 which also conducts melt being forced therethrough into the expansion chamber 23. An inert fluid such as the nitrogen supply 16, under pressure, controlled in its flow by a valve 18 and measured by an orifice 19, then heated to a desirable temperature in a heat exchanger 20, also extending into the chamber 12 and therein into the conduit 13. The gas is advantageously utilized both as a de-monomerizing assistant and as a flow effecting medium effecting a lift of the flowing melt through the conduit 13 into the chamber 23. As the heated nitrogen forces the melt through the conduit 13 it tends to pick up monomers from the melt releasing them into the expansion chamber 23 from where both the nitrogen gas and the monomers are withdrawn.

The expansion chamber 23 has an outwardly, circularly expanding base 25 onto which the melt overflows in a spreading manner by gravity. The melt is continually removed through an outlet 26 positioned at the lowest point of the chamber 23. The chamber 23 is exhausted by means of a vacuum through the conduit 29, the exhaust being passed through the condenser 27.

Monomers and vapors are further released by sweeping the expanded and thinned out melt with superheat steam supplied through conduit 30, the steam released monomers and the nitrogen gas being evacuated, then later condensed. Advantageously, the steam sparger 31 is located above the outlet of the conduit 13 which charges the chamber 23 with melt. Some eruption may occur as the nitrogen gases are released and whatever melt may be upwardly carried will be deflected by the sparger 31.

The melt, free of undesirable quantities of monomers and of vapors, flows through the chamber outlet 26 to an extrusion device (not shown).

The temperatures of superheat steam, nitrogen gas,

and of the melts are closely controlled within desirable ranges for effecting the greatest release of monomers and of vapor. The entire apparatus is lagged for a close temperature control. The operation herein recited can be under atmospheric pressures butis more. desirable that the chamber 23 be under vacuum. for more effective release and evacuation of the chamber.

Particular advantages are derived where the treatment.

at a temperature equal to and preferably greater, than.

the temperature of the polyamide melt, depending upon the degree of polymerization and the proportion of lactarns in the melt. The melting temperature of the polymer may be between 210 C. and220 C. However, to accelerate the rate of removal it is found advantageous to maintain the melt at temperatures substantially above the melting point, e.g., between 230 C. and 260 C. and accordingly, employing similar or greater temperatures for the steam.

It is also found particularly advantageous to charge the expanding chamber 23 with polymer moved thereto by nitrogen gas under pressure. This gas facilitates the removal of lactam monomers While, simultaneously, effecting a flow of the melt into the expansion chamber. The temperature employed for such an inert gas is'within the range of that for the melt, or about equal to that of the superheated steam.

The duration of treatment of the flow under the above conditions may be varied depending upon the amount of lactam desired in the spun product. 'Ihus,proportions of lactarn from 3 up to 5 or 6% by weightnot only may be tolerated but may be advantageous in their, efiect on spinning and the character of the product. It is preferred; however, to reduce the lactam content to below about 4%.

I claim:

1. In themanufacture of synthetic fibers a process for the elimination of undesirable unpolymerized quantities of monomers prior to melt extrusion of a fiber forming polyamide in melt .form derived from the polymeriza- 4 tion of e-caprolactam, e-amino caproic acid and the like which comprises effecting a flow of melt at a predetermined temperature and containing unpolymerized monomers to a spreading out area within a chamber, by direct contact with a heated inert gas under pressure capable of carrying off unpolymerized monomer to raise the melt to said spreading outarea and to maintain said melt at said: predetermined temperature, releasing said inert gas intosaid chamber while spreading said polymer melt to present a thinned section and increased area for exposure to direct contact with super-heated steam for further release of said unpolyrnerizedmonomers, subjecting the spread polymer melt to a sweeping action of the steam, meanwhilewithdrawing the saidinert gas and steam and released monomers from said chamber, and meanwhile withdrawing said melt from said chamber at the predetermined temperature.

2. The process in accordance with claim 1 which the heated inert gas is nitrogen.

References Cited in the file of this patent UNITED STATES PATENTS 509,749 Morrell Nov. 28, 1893 1,678,819 Koch July 31, 1928 1,917,841 Hughes July 11, 1933 2,049,247 Burkhard' July 28, 1936 2,179,833 Sondermann Nov. 14, 1939 2,274,802 Mills Mar. 3, 1942. 2,328,892 Colgate et a1. Sept. 7, 1943 2,561,394 Marshall; July. 24, 1951 2,562,796 Koch July 31, 1951. 2,571,975 Waltz Oct. 16, 1951 2,687,552 Gabler Aug. 31, 1954 2,719,776; Kummel Oct. 4, 1955 FOREIGN PATENTS 579,231 Germany June 22, 1933 172,614 Austria Sept; 25, 1952 172,909 Austria Oct. 25, 1952 OTHER REFERENCES- Johnson et al.: Monomer Recovery in GR-S Manufacture ChemicalEngineering Progress, June 1949, vol. 45, N0. 6, McGraw-Hill. 

1. IN THE MANUFACTURE OF SYNTHETIC FIBERS A PROCESS FOR THE ELIMINATION OF UNDERSIRABLE UNPOLYMERIZED QUANTITIES OF MONOMERS PRIOR TO MELT EXTRUSION OF A FIBER FORMING POLYAMIDE IN MELT FORM DERIVED FROM THE POLYMERIZATION OF E-CAPROLACTAM, E-AMINO CAPROIC ACID AND THE LIKE WHICH COMPRISES EFFECTING A FLOW OF MELT AT A PREDETERMINED TEMPERATURE AND CONTAINING UNPOLYMERIZED MONOMERS TO A SPREADING OUT AREA WITHIN A CHAMBER, BY DIRECT CONTACT WITH A HEATED INERT GAS UNDER PRESSURE CAPABLE OF CARRYING OFF UNPOLYMERIZED MONOMER TO RAISE THE MELT TO SAID SPREADING OUT AREA AND TO MAINTAIN SAID MELT AT SAID PREDETERMINED TEMPERATURE, RELEASING SAID INERT GAS INTO SAID CHAMBER WHILE SPREADING SAID POLYMER MELT TO PRESENT A THINNED SECTION AND INCREASED AREA FOR EXPOSURE TO DIRECT CONTACT WITH SUPER-HEATED STEAM FOR FURTHER RELEASE OF SAID UNPOLYMERIZED MONOMERS, SUBJECTING THE SPREAD POLYMER MELT TO A SWEEPING ACTION OF THE STEAM MEANWHILE WITHDRAWING THE SAID INERT GAS AND STEAM AND RELEASED MONOMERS FROM SAID CHAMBER, AND MEANWHILE WITHDRAWING SAID MELT FROM SAID CHAMBER AT THE PREDETERMINED TEMPERATURE. 